On the 30th August 1548, Katherine Parr gave birth to her first (and only) child at Sudeley Castle in Gloucestershire. She was the famous wife that ‘survived’ Henry VIII and so was Queen Dowager at the time, as well as wife of Thomas Seymour. Thomas and Katherine named her Mary after Katherine’s stepdaughter, Mary Tudor.
Mary Seymour was born healthy, despite both Thomas and Katherine being a little old to be having their first child. At first, it seemed as though Katherine had come through the birth well. However, within a few days, she developed a fever and became weak. These were the first signs of puerperal fever, which afflicted many women of that time. She died on the 5th September, just six days after the birth of her daughter.
Mary was made an orphan by her father’s execution on the 20th March 1549. She was left in the care of Katherine Willoughby, Duchess of Suffolk, who appears to have resented this. On the 22nd January 1550, less than a year after her father’s death, application was made in the House of Commons for the restitution of Lady Mary Seymour. She was made eligible by that act to inherit and remaining property that had not been returned to the Crown at the time of her father’s attainder.
Mary never claimed any remaining part of her father’s estate and her grant from the council was not renewed in September 1550, when it would have been due. Linda Porter says that we can then assume that, in the absence of any further reference, that she was dead by the time of her second birthday.
Katherine the Queen: The Remarkable Life of Katherine Parr, Linda Porter, 2011, p320
On This Day in Tudor History, Claire Ridgway, 2012, p405-406
Portraits of Thomas Seymour and Katherine Parr.